Hermes: a Deficit in the Surface Brightness of the Cosmic Infrared Background Due to Galaxy Cluster Gravitational Lensing

We have observed four massive galaxy clusters with the SPIRE instrument on the Herschel Space Observatory and measure a deficit of surface brightness within their central region after removing detected sources. We simulate the effects of instrumental sensitivity and resolution, the source population, and the lensing effect of the clusters to estimate the shape and amplitude of the deficit. The amplitude of the central deficit is a strong function of the surface density and flux distribution of the background sources. We find that for the current best fitting faint end number counts, and excellent lensing models, the most likely amplitude of the central deficit is the full intensity of the cosmic infrared background (CIB). Our measurement leads to a lower limit to the integrated total intensity of the CIB of I250μm > 0.69 +0.03 −0.03(stat.) +0.11 −0.06(sys.)MJy sr , with more CIB possible from both low-redshift sources and from sources within the target clusters. It should be possible to observe this effect in existing high angular resolution data at other wavelengths where the CIB is bright, which would allow tests of models of the faint source component of the CIB. Subject headings: cosmic background radiation [email protected] † Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. 1 California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 2 Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 3 Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK 4 Dept. of Physics & Astronomy, University of California, Irvine, CA 92697 5 Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu CNRS Université Paris Diderot, CE-Saclay, pt courrier 131, F-91191 Gif-sur-Yvette, France 6 Institut d’Astrophysique Spatiale (IAS), bâtiment 121, Université Paris-Sud 11 and CNRS (UMR 8617), 91405 Orsay, France 7 Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK 8 Center for Astrophysics and Space Astronomy 389-UCB, University of Colorado, Boulder, CO 80309 9 Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, 28691 Madrid, Spain 10 Astronomy Centre, Dept. of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK 11 Department of Physics, Virginia Tech, Blacksburg, VA 24061 12 Dept. of Astrophysical and Planetary Sciences, CASA 389UCB, University of Colorado, Boulder, CO 80309 13 School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK 14 Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada 15 Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR7326, 13388, France 16 Laboratoire d’Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland